1. Field of the Invention
The invention relates generally to a method of storing and releasing heat utilizing a decomposable heat storage material. More particularly, it is directed to a method of utilizing solar energy.
2. Prior Art
Heat storage is known, and various methods have been suggested heretofore for such storage. It has been suggested, for example, that a solid or liquid material be heated to a high temperature and the sensible heat content of the material thereafter used when required. Suggested materials include gravel, rocks and water. The heat storage capability of such materials is relatively low. Thus, such processes are basically impractical in that they require a large bulk to provide storage capacity for significant quantities of heat. More recently, systems have been proposed wherein the heat of solution or heat of fusion is utilized. For patents relating to use of the heat of solution of hydrates, see U.S. Pat. Nos. 2,677,664, 2,706,716 and 2,827,438. For patents relating to use of the heat of fusion for storing thermal energy see U.S. Pat. Nos. 2,677,243, 2,856,506 and 3,320,408.
In U.S. Pat. No. 2,808,494 there is suggested a heat storage method which utilizes as the heat storage medium an anhydrous crystalline solid which is dimorphic, i.e., changes from one anhydrous crystalline form to another on the application of heat. Patentee discloses that the heat storage material is capable of storing as much as 180 Btu/lb. Obviously, however, a substantial quantity of such material still would be required to store a large amount of thermal energy.
In a book entitled Direct Use of the Sun's Energy by Farrington Daniels, New Haven and London, Yale University Press, 1964, and references cited therein, there is compiled a discussion of the various methods proposed for collecting and storing solar energy. Numerous methods of storing and recovering thermal energy are suggested, such as the hydration of various oxides and chlorides, including the oxides of calcium and magnesium. The book, while broadly suggesting that such materials might be used, offers very little specific guidance as to any method by which such materials might be effectively utilized in the storage of thermal energy.
In U.S. Pat. No. 3,642,059, there is disclosed a compact heating and cooling apparatus. The apparatus comprises two vessels connected by a conduit, the first containing a vaporizing liquid (water), and the second containing a vapor-absorptive chemical (Na.sub.2 O). The liquid evaporates from the first vessel and its vapors are drawn by the vapor-absorptive chemical through the conduit to the second vessel where they are absorbed and condensed with the subsequent cooling of the first vessel through heat of vaporization and heating of the second vessel through heat of vapor absorption. Other vapor-absorptive materials disclosed in the patent include lithium monoxide, calcium monoxide, calcium chloride, phosphorus pentoxide, and sodium hydroxide. Patentee's apparatus is intended for use in remote isolated areas devoid of electricity or other conventional forms of energy, and he teaches that a low temperature, i.e., below about 120.degree.C must be maintained in the two vessels for effective operation. Such apparatus is of limited utility.
There still is a need for an effective cyclic method of storing and recovering substantial quantities of thermal energy for heating large areas such as office buildings, or homes, to generate steam for load leveling in the utility industries and the like.